Touch sensors are applied in different technical fields. They offer the possibility of controlling a device by simply touching a predefined area of a surface like an operation screen. For that, often a change in “common mode” capacitance to ground is used. In contrast to that, near field imaging reacts on local field changes and not to a “common mode” capacitance to ground. Therefore, near field imaging provides a more reliable way of operating a touch sensor compared to standard touch sensors operated in a “common mode” technique. Further, near field imaging allows to detect not only the approach of an external object like a finger but also the object's positions. Thus, for example, near field imaging also allows for controlling a system with the help of a touch screen sensor by pointing onto different screen areas with respective functions with a finger tip. According touch sensors a widely known in different technical fields.
From US 2003/0159910 A1 a combination of a capacitive touch sensor and an OLED device is known. The primary purpose of the device described in this document is to provide an integrated illuminated touch sensor device. In this OLED device at least one electrode of the touch responsive switching device is coupled to at least one electrode of the light emitting device.
However, it is known that touch sensor devices which are operated according to the principles described above are failure-prone, especially in harsh environmental conditions. This is due to the fact that a detection signal is generated when a predefined threshold value has been exceeded, e. g. when the induced current in a capacitive sensor exceeds a threshold value. However, the absolute value might change due to temperature and/or surface conditions of the sensor device. Thus, the touch sensor device might not be reliable enough.